Some of the new generation of handheld electronic devices include both a camera and a Global Positioning System (GPS) receiver chipset. Examples of these handheld electronic devices include GPS-enabled wireless communications devices, PDA Pocket PCs or tablets, GPS-enabled camera-phones or smart phones, and GPS-enabled cameras. These devices can be made “location-aware” by virtue of a GPS receiver that is either embedded as a GPS chipset or connected externally, e.g. a Bluetooth™-enabled GPS puck.
The combination of GPS and camera features enables “geotagging” {or “geocoding”) of digital photographs, i.e. tagging digital photos with geographical information indicative of the location at which the photo was taken. For example, the geotagging may involve appending coordinates of longitude and latitude to a metadata tag, e.g. an Exchangeable Image File Format (EXIF) tag, that is associated with the digital photo.
Conventionally, for geotagging to be accurate and meaningful, the GPS receiver should be locked at the time the photo is taken, i.e. the GPS receiver must have acquired a position fix, so that the current position data (e.g. position coordinates) can be written to the metadata tag associated with the digital photo.
As is known in the art, a GPS lock or position fix is acquired by synchronizing with at least four GPS satellite vehicles in orbit. The time required to compute the location on a new synchronization is known as the time-to-first-fix (TTFF). Unfortunately, the TTFF can be frustratingly long for various reasons, including poor sky access (e.g. the urban canyon effect or dense overhead foliage) or out-of-date almanac or ephemeris data on start-up.
In order to be able to find the satellites initially, a GPS receiver normally requires an almanac of satellite location data that is imprecise but valid for several months. If a full reset occurs, then downloading the full almanac takes 12.5 minutes, with a maximum wait of 25 minutes. The almanac serves as a rough approximation of satellite location. To acquire a precise fix, the device must also obtain ephemeris data from each satellite itself which consists of very precise orbital and clock correction data, at a slow 50 bytes per second for a total of 12 seconds for ephemeris and 6 seconds for clock corrections. When the device retrieves this data directly from a satellite broadcast, it is operating in autonomous or standalone GPS mode, the most common mode of operation. The ephemeris data is cached by the receiver, but it becomes stale and unusable within 3 to 4 hours due to satellite drift due to various sources of error. If the wireless handheld device loses synchronization because, for example, the user enters a building or subway and the ephemeris becomes stale, then a warm or cold start condition occurs and new ephemeris must be downloaded again through a full sky search.
In addition to the latency involved in the data download, obstructions in the signal path can further prolong the TTFF. Satellites broadcast their ephemeris every 30 seconds, 5 times per window. If the signal is interrupted, the receiver must wait for another cycle. Obtaining a fix can easily take several minutes or much longer if the user is travelling through an urban canyon or dense foliage. On a hot start, where current ephemeris data is still available, the time required to obtain a fix is reduced to seconds. However, on a warm start, if a user turns on the handheld device or emerges from a building so that the receiver has no valid ephemeris data in memory, then the user may typically need to wait a few minutes before a fix is established. Of course, if both the almanac and ephemeris is out-dated, i.e. a cold start, then the TTFF can be frustratingly long.
These TTFF delays preclude the immediate geotagging of photos. If the user wishes to take a geotagged photo, the camera either remains locked (“frozen’) until the GPS position fix is obtained, or the photo is taken without GPS lock, in which case the photo cannot be geotagged at that point because a GPS fix is unavailable. Thus, if, after the photo is taken, the user moves substantially away from the geographical location where the photo was taken, then any subsequent GPS position fix is potentially of limited positional accuracy in attempting to retroactively geotag the photograph.
It will be noted that throughout the appended drawings, like features are identified by like reference numerals.